Mixing devices for plastics materials

ABSTRACT

In a mixing device for plastic material a body extends substantially over the entire cross section of a flow passage through which the material flows when in use. The body comprises first and second groups of passages for the material extending through the body. Each passage is parallel to the other passages in the same group and alternates with passages in the other group. The inlet and outlet ends of the passages of the first group are disposed on one and the other side respectively of a central longitudinal plane through the body. The inlet and outlet ends of the passages of the second group are disposed on said other and said one side respectively to said plane. The groups of passages cross over in a central region of the body such that in use temperature equalization of the material is promoted in said region.

United States Patent Upmeier 51 Aug. 8, 1972 [72] Inventor: Hartmut Upmeier, Zum Kahlen Berg [1, 4542 Tecklenburg, Germany [22] Filed: May 20, 1970 [21] Appl. No.: 38,958

[30] Foreign Application Priority Data May 23, 1969 Germany ..P 19 26 488.] Oct. 28, 1969 Germany ..P 19 54 242.8

[52] 11.8. CI ..259/4, 138/37 [51] Int. Cl. ..B0lf 5/00 [58] Field of Seareh............l8/8 SC, DIG. 49; 259/4; 138/37, 39, 42

[56] References Cited UNITED STATES PATENTS 2,584,827 2/ 1952 Bailey ..259/4 3,546,739 12/ 1970 Callahan et al ..259/4 X 1,419,216 6/1922 Burckhardt ..48/180 Primary Examiner-Robert W. Jenkins Assistant Examiner-Philip R. Coe

Altorney-Fleit, Gipple & Jacobson [57] ABSTRACT In a mixing device for plastic material a body extends substantially over the entire cross section of a flow passage through which the material flows when in use. The body comprises first and second groups of passages for the material extending through the body. Each passage is parallel to the other passages in the same group and alternates with passages in the other group. The inlet and outlet ends of the passages of the first group are disposed on one and the other side respectively of a central longitudinal plane through the body. The inlet and outlet ends of the passages of the second group are disposed on said other and said one side respectively to said plane. The groups of passages cross over in a central region of the body such that in use temperature equalization of the material is promoted in said region.

19 Claims, 9 Drawing Figures PATENTED MI 8 I972 SHKEI 1 OF 3 INVENTOR HortmutUPMElER his ATTORNEYJ PATENTEDAUE 8 I972 SHEET 2 [IF 3 FIGA PATENTEU M1 8 19?? SHEET 3 [If 3 FIGS INVENTOR Hurtmut UPMEIER is ATTORNEYS MIXING DEVICES FOR PLASTICS MATERIALS This invention relates to mixing devices for plastics materials.

In the manufacture of articles made of plastics materials, in particular thermoplastic or non-crosslinlted elastomeric materials, the uniformity of viscosity and temperature of the material over the entire crosssection of the delivery passage to the forming tool is an essential condition for achieving balanced properties in the finished articles. Thus for example low internal stresses are necessary for the best possible dimensional constancy in the case of parts produced by injection moulding, or close tolerances in the case of films produced by extrusion presses.

In all the processing machines used for this purpose, such as for example piston presses, screw-piston injection-moulding machines, screw-piston hollow body blowing machines and screw extrusion presses, it has been found that the viscosity and the temperature of the material is not uniform over the entire cross-section of the delivery passage leading to the forming tool. Even therefore where the forming tool is dimensionally perfect, there occur variations in the dimensions of the finished articles or poor tolerances in respect of thickness of films.

In the piston extrusion presses which were previously frequently used, the material was heated and plasticized only by external heating means, thus resulting in a very irregular temperature and viscosity. In order to improve this, various insertion members are known in which a better contact between the material and the heated cylinder wall is established by displacing the material with so-called torpedos. In many cases these torpedos were provided with projections which were intended to ensure better plasticization of the material by changing its direction of flow.

A substantial improvement in plasticization of the material was achieved by using screw presses which heat the material by mixing and internal friction. By taking temperature measurements in the connecting passage between the end of the screw and the forming tool however, it has been found that the temperature profile over the cross-section shows considerable differences. Generally, this temperature profile has a radially symmetrical temperature peak in the central region due to the flow mechanisms upstream of the end screw, while a further radially symmetrical, annular temperature peak is to be found due to the influences of wall friction.

Although the above described unfavorable effects on the quality of the finished articles occur, there is in general no particular flow problem when using a radially symmetrical forming too], because the temperature variations are distributed uniformly over the entire periphery. However, when using forming tools with unsymmetrical flow paths, both the differences in the flow behavior of the material and also the dimensional variations in the finished articles may be considerable. This affects virtually all injection tools with lateral delivery of material, which are required for a large pro portion of articles produced. This disadvantageous phenomena are further increased if a distributor member, for example of T-shape, is used to divide the material into two or more portions, with the corresponding number of injection tools, as in that case each individual portion of material has a radially unsymmetrical temperature distribution.

According to the present invention there is provided a mixing device for plastics material, comprising a body extending over substantially the entire cross-section of a flow passage through which in use the material flows, the body including first and second groups of passages for the material extending through the body, each passage being parallel to the other passages in the same group and alternating with passages in the other group, the inlet and outlet ends of the passages of the first group being on one and the other side respectively of a central longitudinal plane through the body, and the inlet and outlet ends of the passages of the second group being on said other and said one side respectively of said plane, whereby the groups of passages cross over in a central region of the body such that in use temperature equalization of the material is promoted in said region.

Because the passages are arranged parallel to each other in each group and are distributed over the entire flow crosspsection of the flow passage, the free flow cross section of a mixing device according to the intention can amount to 50 percent of the area of the flow passage, so that the flow resistance and thus the undesired increase in temperature of the material can be restricted to a minimum. As the passages all cut said plane, while the inlet and outlet ends of adjacent passages are alternately displaced relative to said plane towards the one and the other side, and the passages are led past each other in the central region in which they cross, use is made of the principle of the flat-flowcross-flow-heat-exchanger, which provides for intensive radial equalization of temperature of the partial flows.

The effect of the mixing device according to the invention can be varied within wide limits by suitable selection of the thickness of the passages so that the optimum design be found, even for widely different types of plastics material. The mixing member according to the invention can be fitted into a forming tool directly upstream of the inlet bore so that there cannot be any renewed changes in temperature of the material downstream of the mixing member, before the mate rial passes into the forming tool.

In a further aspect of the invention, the passages can with particular advantage be formed by the spaces between flat plates which are stacked one upon the other in layers in opposed directions and which are preferably only about 1 to 2 mm thick so that the flows of material passing into the central region in which the flows cross are also very thin and complete temperature equalization is promoted. The plates desirably end in sharp edges at the inlet and outlet ends of the passages, in order to provide transitional regions which are favorable to the flow of material.

In accordance with a further proposal of the invention, the stack of plates can be releasably or nonreleasably held together by pins.

By reason of the mixing body being constructed of flat plates, the material is only mixed about one main axis, which gives a sufficient temperature equalization effect for normal uses. If even more complete equalization is desired, two mixing devices can be arranged one behind the other in the flow passage, said planes of the two mixing devices being arranged at an angle of relative to each other.

The mixing device can also be fitted into a distributor, the passages in this case leading into difierent discharge pipes. With this arrangement it is again possible to insert a further mixing device in each discharge pipe, said planes of the mixing devices being suitably oriented to provide complete temperature equalization.

As the inclusion of the mixing device in the flow passage causes an additional resistance to flow which may in some cases be unacceptable, for example because of an undesirable increase in the frictional heat generated by the conveyor screw, the mixing device can be arranged in a portion of the flow passage which is enlarged, preferably conically, in cross-section, so that the total cross-section of the passages is equal or substantially equal to the cross-section of the flow passage upstream of the enlarged portion.

In the central region in which the passages cross they can merge into each other without intermediate walls. In the case of larger mixing devices for higher rates of material through-put however, it has been found that the individual flows of material which pass out of the passages into the central region could flow parallel to and beside one another through the central region, without the desired crossing effect. In order to prevent this undesired occurrence in the case of larger mixing devices, the flows of material can be separated from each other in the central region by highly heat-conductive intermediate walls which are thin in relation to the thickness of the plates forming the passages. These intermediate walls permit and compel equalization of the temperature in the material as they offer no substantial resistance to the transfer of heat and they prevent any change in direction of the individual flows.

When, in accordance with the above preferred embodiment, the passages are formed by the spaces between plates which are stacked one upon the other in layers in opposed directions, the intermediate walls can comprise thin separating plates which are arranged between the consecutive plates and which extend in contact thereto over the entire height of the mixing device. In another embodiment however, the individual plates of the mixing body can also comprise plates of suitable thickness, with incorporated crossed passages, the passages being separated from each other in the region in which they cross by thin intermediate walls produced by a milling operation.

Three mixing devices in accordance with the present invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 shows a view on to one of the end faces of the first mixing device,

FIG. 2 shows a section taken along the line lI-II of FIG. 1,

FIG. 3 shows a section taken through the mixing device in the plane of the line III-III of FIG. 1,

FIG. 4 shows a section of the second mixing device taken along the lines IV-IV of FIGS. 5 and 6,

FIG. 5 shows on the left-hand side a view in the direction of the arrow A and on the right-hand side a section taken along the line V-V of FIG. 4,

FIG. 6 shows on the left-hand side a view in the direction of the arrow B and on the right-hand side a section taken along the line Vl--Vl of FIG. 4,

FIG. 7 shows a view on to one of the end faces of the third mixing device according to the invention,

FIG. 8 shows a section taken along the line VII]- VIII of FIG. 7, and

FIG. 9shows a section in the plane of the line lX-l X of FIG. 7.

The mixing device shown in FIGS. I to 3 is preferably fitted into a recess I in the flow passage l upstream of the inlet connection 2 of a forming tool (not shown). It is made up of individual flat plates 3 which are stacked together in layers in opposed directions with similar plates 3'. thus forming between the individual layers, passages 4 and 4' which cross in opposed directions and which each cut the central longitudinal plane .x-x of the flow passage I. In accordance with the invention, the flows of material flowing in the passages 4 and 4' cross in the region 5 without intermediate walls, the region 5 being approximately rhombic depending on the particular dimensions selected, thus resulting in virtually complete temperature equalization of the material.

As the individual plates 3 and 3' which have material passing over them on both sides are not subject to pressure, they can be made as thin as desired and accordingly produce thin layers of material so that the heat-exchange effect is ensured. The plates 3 and 3' are preferably made in a thickness of from I to 2 mm. The provision of sharp edges 6 and 6' at the inlet and outlet edges of the plates 3 and 3' provide for a smooth flow.

The external shape of the plates 3 and 3' depends on the shape of the flow passage I in which the mixing device is fitted. In the embodiment illustrated which has a flow delivery passage 1, the height of the plates 3 and 3' gradually decreases and the inlet and outlet orifices of the passages 4 and 4' between the plates 3 and 3' conform to the lesser height. The entire stack of plates 3 and 3' is clamped together and machined jointly, thus providing a precise external fitting shape. In the case of a rectangular or square flow passage 1, the plates 3 and 3' can advantageously be produced by stamping out.

The position of the plates 3 and 3 relative to each other is fixed by pins 7. If the mixing device is dismantable for cleaning purposes, the pins 7 can be fitted without lateral securing means as the mixing device is held together after installation by the passage wall I. As the mixing device does not have any dead comers due to the configuration of the passages 4 and 4, it does not need to be cleaned even when a change in color is made, as in such a case it can be flushed free immediately. Therefore the plate 3 and 3' can also be riveted together by the pins 7. It is also possible for the pins 7 to be in the form of countersunk-head screws.

The passages 4 and 4 can also be milled or bored out of the solid, although this involves considerably higher production costs relative to the construction using separate plates, as in general all surfaces over which material is passed must be polished.

By reason of the mixing device being made up of flat plates, the extrusion material is only mixed about one main axis, which provides a satisfactory temperature equalization effect for normal uses. If complete equalization is necessary, two mixing devices can be arranged one behind the other, the central plane x-x of the second mixing device being turned through relative to the central plane x-x of the first mixing device.

As the incorporation of the mixing device in the flow passage 1 causes an additional resistance to be produced, temperature equalization can be effected by incorporating a mixing device of larger size, in which case the delivery passage 1 is advantageously conically enlarged to correspond to the size of the mixing device.

The further embodiment of the invention idea, as illustrated in H68. 4 to 6, relates to a T-shaped distributor member with the second mixing device according to the invention structurally incorporated therein. In this distributor mixing device, the mixing device which again comprises plates 3 and 3' is fitted for example into a milled-out recess 8 in the closure plug 9 and releasably fixed, screwed or riveted by pins 7, as described hereinbefore. The milled guide surfaces 10 give a transistion which is favorable from the flow point of view, from the larger flow passage 11 to the size of the mixing device which is adapted to the dimensions of the two outlet passages 12, 12'.

In accordance with the invention, the passages 4 and 4' are not brought together but are passed out laterally in opposite directions, where the sharp edges 13 and 13' give a smooth transistion into the outlet passages 12 and 12'. The outlet passages 12 and 12' arranged on opposite sides produce the function of a direction changing-distributor member with a mixing action. Different configurations of the plates 3 and 3 likewise make it possible for other angles between the passages 11,12 and 12' to be achieved.

A theoretically complete temperature equalization in the material flowing through the mixing device is effected if, after division of the flow of material into a two separate discharge passages, a respective mixing device with its main axis turned through 90 relative to the main axis of the distributor-mixing device is fitted upstream of the inlet into the forming tool.

FIGS. 7 to 9 show a mixing device made up of plates and having thin interposed separating plates. The construction is substantially the same as in the embodiment shown in FIGS. 1 to 3. interposed between the individual plates 3 and 3 are thin separating plates 14 made of a highly heat-conductive material, so that any mixing of the crossed flows of material is prevented in the region 5 in which they cross, but on the other hand the desired heat exchange is achieved as the thin separating plates 14 readily permit the heat exchange. The through-fiow passages could however also be milled in plates which extend over the entire height of the mixing device.

l claim:

1. A mixing device for plastics material, comprising a body extending over substantially the entire cross-section of a flow passage through which in use the material flows, the body including first and second groups of passages for the material extending through the body, each passage being parallel to the other passages in the same group and alternating with passages in the other group, the inlet and outlet ends of the passages of the first group being on one and the other side respectively of a central longitudinal plane through the body, and the inlet and outlet ends of the passages of the second group being on said other and said one side respectively of said plane, each of said passages being formed by a space between a pair of flat walls arranged side by side and spaced by the desired width of said passage, each wall of said pair of walls tapering towards one end thereof, the tapered end of one wall of said pair of walls being located at the entrance end of said body and the tapered end of the other wall of said pair of walls being located at the exit end of said body, the locations of said tapered ends of each wall of said pair of walls alternating with each adjacent one of said passages such that each passage is interrupted by a free space in a central region of said body where said groups of passages cross over so that in use temperature equalization of the material is promoted in said region.

2. A mixing device according to claim 1 wherein said pairs of walls are formed by plates which are stacked one upon another in layers to form said groups of passages.

3. A mixing device according to claim 2 wherein the plates are from I to 2 mm thick.

4. A mixing device according to claim 2, wherein the stack of plates is held together by pins.

5. A mixing device according to claim 2 wherein a thin separating plate extends over the entire height of the mixing device between each two adjacent pairs of plates.

6. A mixing device according to claim 1 wherein said walls terminate in sharp edges at said inlet and outlet ends.

7. A mixing device according to claim I inserted in a distributor member such that said first and second groups of passages lead into different respective discharge passages.

8. A mixing device according to claim 1 wherein said body is disposed in a portion of the flow passage of enlarged cross-section.

9. A mixing device according to claim 8 wherein the total cross-sectional area of the inlet ends of said groups of passages is equal to the cross-section of the flow passage upstream of said body.

10. A mixing device according to claim 1 wherein the flows of material in said central region are separated from each other by highly heat-conductive intermediate walls which are thin in relation to the thickness of said walls forming said groups of passages.

11. A mixing device according to claim 1 wherein said groups of passages are milled in plates which extend over the entire height of the mixing device.

12. A mixing arrangement comprising two mixing devices according to claim 1 arranged one behind the other in a common flow passage with said central planes at to one another.

13. A mixing device for plastics material, comprising a body extending over substantially the entire crosssection of a flow passage through which in use the material flows, the body including first and second groups of passages for the material extending through the body, each passage being parallel to the other passages in the same group and alternating with passages in the other group, the inlet and outlet ends of the passages of the first group being on one and the other side respectively of a central longitudinal plane through the body, and the inlet and outlet ends of the passages of the second group being on said other and said one side respectively of said plane, whereby the groups of passages cross over in a central region of the body such that in use temperature equalization of the material is promoted in said region, said groups of passages being formed by spaces between plates which are stacked one upon another in layers and wherein the plates terminate in sharp edges at said inlet and outlet ends.

14. A mixing device according to claim 13 wherein the stack of plates is held together by pins.

15. A mixing device according to claim 13 inserted in a distributor member such that said first and second groups of passages lead into different respective discharge passages.

16. A mixing device according to claim 13, wherein said body is disposed in a portion of the flow passage of enlarged cross-section.

17. A mixing device according to claim 16, wherein the total cross-sectional area of the inlet ends of said groups of passages is equal to the cross-section of a flow passage upstream of said body.

18. A mixing device according to claim 13 wherein the flows of material in said central region are separated from each other by highly heat-conductive intermediate walls which are thin in relation to the thickness of the plates forming said groups of passages.

19. A mixing device according to claim 13 wherein a thin separating plate extends over the entire height of the mixing device between each two adjacent pairs of plates.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Dated August 8,

Patent No Inventor(s) HARTMUT UPMEIER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the title page, insert [73] Assignee: Windmoller & Holscher Lengerich of Westphalia Germany Signed and Sealed this 3rd day of April 1973.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.PLETCHER,JR.

Commissioner of Patents Attesting Officer USCOMM-DC 6O376-P69 U 5. GOVERNMENT PRINHNG OFFICE I959 O355'334 

1. A mixing device for plastics material, comprising a body extending over substantially the entire cross-section of a flow passage through which in use the material flows, the body including first and second groups of passages for the material extending through the body, each passage being parallel to the other passages in the same group and alternating with passages in the other group, the inlet and outlet ends of the passages of the first group being on one and the other side respectively of a central longitudinal plane through the body, and the inlet and outlet ends of the passages of the second group being on said other and said one side respectively of said plane, each of said passages being formed by a space between a pair of flat walls arranged side by side and spaced by the desired width of said passage, each wall of said pair of walls tapering towards one end thereof, the tapered end of one wall of said pair of walls being located at the entrance end of said body and the tapered end of the other wall of said pair of walls being located at the exit end of said body, the locations of said tapered ends of each wall of said pair of walls alternating with each adjacent one of said passages such that each passage is interrupted by a free space in a central region of said body where said groups of passages cross over so that in use temperature equalization of the material is promoted in said region.
 2. A mixing device according to claim 1 wherein said pairs of walls are formed by plates which are stacked one upon another in layers to form said groups of passages.
 3. A mixing device according to claim 2 wherein the plates are from 1 to 2 mm thick.
 4. A mixing device according to claim 2, wherein the stack of plates is held together by pins.
 5. A mixing device according to claim 2 wherein a thin separating plate extends over the entire height of the mixing device between each two adjacent pairs of plates.
 6. A mixing device according to claim 1 wherein said walls terminate in sharp edges at said inlet and outlet ends.
 7. A mixing device according to claim 1 inserted in a distributor member such that said first and second groups of passages lead into different respective discharge passages.
 8. A mixing device according to claim 1 wherein said body is disposed in a portion of the flow passage of enlarged cross-section.
 9. A miXing device according to claim 8 wherein the total cross-sectional area of the inlet ends of said groups of passages is equal to the cross-section of the flow passage upstream of said body.
 10. A mixing device according to claim 1 wherein the flows of material in said central region are separated from each other by highly heat-conductive intermediate walls which are thin in relation to the thickness of said walls forming said groups of passages.
 11. A mixing device according to claim 1 wherein said groups of passages are milled in plates which extend over the entire height of the mixing device.
 12. A mixing arrangement comprising two mixing devices according to claim 1 arranged one behind the other in a common flow passage with said central planes at 90* to one another.
 13. A mixing device for plastics material, comprising a body extending over substantially the entire cross-section of a flow passage through which in use the material flows, the body including first and second groups of passages for the material extending through the body, each passage being parallel to the other passages in the same group and alternating with passages in the other group, the inlet and outlet ends of the passages of the first group being on one and the other side respectively of a central longitudinal plane through the body, and the inlet and outlet ends of the passages of the second group being on said other and said one side respectively of said plane, whereby the groups of passages cross over in a central region of the body such that in use temperature equalization of the material is promoted in said region, said groups of passages being formed by spaces between plates which are stacked one upon another in layers and wherein the plates terminate in sharp edges at said inlet and outlet ends.
 14. A mixing device according to claim 13 wherein the stack of plates is held together by pins.
 15. A mixing device according to claim 13 inserted in a distributor member such that said first and second groups of passages lead into different respective discharge passages.
 16. A mixing device according to claim 13, wherein said body is disposed in a portion of the flow passage of enlarged cross-section.
 17. A mixing device according to claim 16, wherein the total cross-sectional area of the inlet ends of said groups of passages is equal to the cross-section of a flow passage upstream of said body.
 18. A mixing device according to claim 13 wherein the flows of material in said central region are separated from each other by highly heat-conductive intermediate walls which are thin in relation to the thickness of the plates forming said groups of passages.
 19. A mixing device according to claim 13 wherein a thin separating plate extends over the entire height of the mixing device between each two adjacent pairs of plates. 